Summary of H2 reduction Process for Oxygen production from
Allen 1996 (carlton.c.allen1@jsc.nasa.gov)
Temperature of process vessel: 1000 - 1050ºC
Amount of feedstock used per experiment: 200 - 300 mg
Length of feedstock exposure to H2: 3 hours
H2 flow rate: 120 cm^3/min … with a 3.8cm diam hole it is: 0.18 cm/sec (H2 is at room temp)
Feedstock Variability for O2 yield:
1. Iron-poor highlands soil: 1-2 wt% O2
2. Mare basaltic soils: 2.5-3.6 wt% O2
3. Iron-rich pyroclastic glass: 4.3-4.6 wt% O2
 Oxygen yield is strongly correlated to initial Fe content in the feedstock. [figure 1 of Allen, 1996]
Regression line: Y = 0.19X + 0.55 where x is initial wt% Fe content, and Y is the wt% of O2
released under the given H2 flow rate and temperature.
 if spend time beneficiating soils to ilmenite, theoretically this process could yield 10 wt% O2 if
using pure ilmenite. Rocks have up to 25wt% ilmenite, more often closer to 10wt%
 Stoichiometric reduction of pyroclastic glass could yield 5.1 wt% O2.
Generalizing:
- Oxygen yield from lunar materials using H2 reduction ranges from ~2 to 5 wt%
- At a yield of 5 wt% a metric ton of O2 could be produced by processing 20 metric tons of
feedstock. Assuming a density of 2.0 g/cm^3, this is equivalent to 10 m^3 of lunar soil.
- during their experiments H2 flowed at 120 cm^3/min for 3 hours to get these yields. This
required 21600 cm^3 of H2 gas (~1 mol of gas) at room temperature.
Their Recommendations:
- H2 flow rate of 1cm/sec
- processing time of 1-3 hours
- at 1hour processing time will get 90% of stoichiometric yield.
- temperature of 1000-1050ºC
- ** Depends highly upon Fe content of the feedstock!!! Higher Fe content, the Higher the amount
of O2 released.
Mass Breakdown for Scaled System (based on component masses from Rosenberg system):
To make this scaled system mass I am basically taking the Rosenberg Batch system for a CH4 reduction
plant:
This Rosenberg CH4 reduction plant is:
Regolith reduction reactor = 52.4 kg
CO reduction reactor =
75.1 kg
Water Electrolysis Unit =
91.7 kg
Oxygen Liquification Unit = 393.0 kg
Oxygen Storage Unit =
167.3 kg
For a H2 reduction reactor a CO reduction process is not needed, so that mass is dropped. We will assume
that the Regolith reduction reactor will need a benefication system (~20kg) to get high Ilmenite feedstock.
All other units will remain the same. So the estimated H2 reduction plant (to create 5 mt of O2/yr) will be:
Benefication system=
20.0 kg
Regolith Reduction reactor = 52.4 kg
Water Electrolysis Unit =
91.7 kg
Oxygen Liquification Unit = 393.0 kg
Oxygen Storage Unit =
167.3 kg
Because the process temperature for H2 reduction is only ~2/3 that of CH4 reduction the power facility for
Regolith reduction reactor will be only 2/3 that of the Rosenberg reactor.
Scaled System to produce 500 kg O2 per year (100000kg regolith /yr or 14.3 kg/hr):
According to Allen [1996] max O2 wt% = 5wt% so max Fe wt% is 18wt% released, but only 10wt% of
any regolith is Ilmenite.
Products (again operating 80% of the time, 7000hrs/yr):
1. 500 kg O2 / yr or 71 g/hr
2. 1800 kg Fe / yr or 257 g/hr
3. 5260 kg TiO2 / yr or 751 g/hr
4. Some other FeO slag etc.
Scale System Masses:
Benefication system = 20.0 kg (doesn’t scale)
Power systemRegolith Reduction Reactor (needs 2.57kW at 125 W/kg) = 20.6 kg *2/3 = 13.7 kg
Water Electrolysis Reactor (needs 1.16 kW at 125 W/kg) = 9.28 kg *2/3 = 6.19 kg
Oxygen Liquification Reactor (0.37 kW at 125 W/kg) = 2.96 kg *2/3 = 1.97 kg
Regolith Reduction Reactor (doesn’t scale) = 52.4 kg
Water Electrolysis Unit (doesn’t scale) = 91.7 kg
O2 Liquification Unit = 393.0 / 10 = 39.3 kg
O2 Storage unit = 167.3 / 10 = 16.7 kg
Subtotal = 242 kg
Add 20% for error and misc mass = 242 * .2 = 48.4 kg
Total Mass for scaled 500 H2 reduction system = 290 kg
Mass of system minus power = 268 kg
Scaled System to produce 100 kg O2 per year (20000kg regolith / yr or 2.86 kg/hr):
Products (operating 7000 hrs/year):
1. 100 kg O2 / yr or 14 g/hr
2. 360 kg Fe / yr or 51 g/hr
3. 1000 kg TiO2 / yr or 150 g/hr
4. Some other FeO slag.
Scaled System Mass:
Benefication System (doesn’t scale): 20 kg
Power SystemRegolith Reduction Reactor (needs 0.514kW at 125 W/kg) = 4.1 kg *2/3 = 2.73 kg
Water Electrolysis Reactor (needs 0.232 kW at 125 W/kg) = 1.86 kg *2/3 = 1.24 kg
Oxygen Liquification Reactor (0.074 kW at 125 W/kg) = 0.59 kg *2/3 = 0.39 kg
Regolith Reduction Reactor (doesn’t scale) = 52.4 kg
Water Electrolysis Unit (doesn’t scale) = 91.7 kg
O2 Liquification Unit = 393.0 / 50 = 7.86 kg
O2 Storage unit = 167.3 / 50 = 3.35 kg
Subtotal = 180 kg
Add 20% for error and other misc mass = 180*.2 = 36 kg
Total Mass for scaled 500 H2 reduction system = 216 kg
Mass of system minus power = 211 kg
My calculations about allen data:
According to Allen:
- slowest case: using 200mg of feedstock and 3 hours per run,
200mg * 8runs/day = 1600mg processed / day
at min efficency (2%) … get 32mg of O2/day
- best case: using 300mg of feedstock and 1 hour per run:
300mg * 24runs/day = 7200mg processed/day
at max efficency (5%) get 360mg of O2/day …. 0.36g/day
NOTE: according to Sauer [Metabolic Support of a Lunar Base, in Space Activities of the 21st Century]
each human needs:
- 3216g of water per day,
- 806g of Oxygen per day.
For a 6 person base this is 4836g of oxygen consumed per day.
At the max rate above:
4836g / 0.36g/day = ~13500days to produce this oxygen. Or ~37 years … Not acceptable
Say there is a 1% loss of oxygen from the system. This means there will be approximately 0.01 *
4836g = ~48.4g O2 lost/day
Say we want a system minimally capable of replacing this lost oxygen.
Therefore at 5% O2 yield rate it must process: 48.4/0.05 = 967g/day
967 / 7.2 = 134 times faster than Allen experiment.
Previous had 11.34 cm^2 crucible hole etc… so 11.34 * 134 = 16715 cm^2 hole, 22cm radius.
Keeping a gas flow rate of 1 cm/sec we get:
3600sec/hr * 1hr/run * 16715cm^3/sec = 60174000 cm^3/run needed of H2
60174000 cm^3 * density of H2 (~0.09g/cm^3) = ~5410kg of H2 needed.
Producing ~48.4g O2 per day it takes 5077 / 48.4 = 105 days to produce total required O2 needed by a 6
man base (4836+5% extra O2 = 5077).
??? Assuming mass of the plant will be scaled at same rate (134 times) we need to find approximate mass
numbers for the plant that Allen used, or estimated mass numbers for a space worth version of the same
plant.
??? Also need power requirement… and how they would scale.